{"id":"CVE-2026-12372","aliases":["GHSA-2jhm-w3mp-jcwr","PYSEC-2026-3955"],"url":"https://o3.security/vulnerability/CVE-2026-12372","summary":"Server-Side Request Forgery (SSRF) in nltk/nltk","details":"A Server-Side Request Forgery (SSRF) vulnerability exists in nltk/nltk versions 3.9.4 and the current develop branch. The `nltk.pathsec.validate_network_url()` function, intended to prevent SSRF by rejecting internal network addresses, fails to reject IPs in the RFC 6598 shared address space (`100.64.0.0/10`). This occurs because Python's `ipaddress` module does not classify such addresses as `is_private` or `is_global`, and the current guard only checks `is_private` and a few explicit categories. An attacker who can influence a URL passed to NLTK's network-loading helpers can exploit this vulnerability to make a strict-mode application send requests to shared-address-space hosts, potentially exposing non-public infrastructure reachable from the application host. The impact is limited to SSRF-style confidentiality exposure, with no code execution claimed.","published":"2026-08-09T22:45:52.799Z","modified":"2026-10-24T10:31:00.384033171Z","cvss":{"score":3.7,"severity":"LOW","vector":"CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"nltk","fixedVersion":"3.10.0"}],"fix":{"url":"https://github.com/nltk/nltk/commit/4a820afa58810cd05049b6c6eae306694d6cfe65","label":"nltk/nltk@4a820af"},"references":[{"type":"WEB","url":"https://huntr.com/bounties/2911b643-571c-42e4-b0c2-9a1fa6f491db"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/12xxx/CVE-2026-12372.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-12372"},{"type":"WEB","url":"https://github.com/nltk/nltk/commit/4a820afa58810cd05049b6c6eae306694d6cfe65"},{"type":"PACKAGE","url":"https://github.com/nltk/nltk"},{"type":"WEB","url":"https://github.com/nltk/nltk/releases/tag/v3.10.0"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3955.yaml"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-24T10:31:00.384033171Z"}}